The search for compositions which have a combination of excellent insecticidal activity and desirable low toxicity to plants and mammals is a continuing one because of factors such as the desire for compounds exhibiting greater insecticidal activity, better selectivity, low environmental impact, low production cost and effectiveness against insects resistant to many known insecticides.
The hydrogenated materials of the present invention are particularly suitable for controlling plant destructive insects in crops of cultivated plants, ornaments and forestry.
Various parts of the neem (or nim) tree, Azadirachta indica have long been used in India for their reputed medicinal or insecticidal properties. This subtropical tree is native to the arid regions of India, Pakistan, Sri Lanka, and parts of Southeast Asia and Africa.
Although all parts of the neem tree appear to have natural resistance to pests and diseases, the seeds appear to have the greatest resistance. Formulations and extracts of the seeds have been shown to be effective against many species of crop pests, including gypsy moths, Japanese beetles, aphids, tobacco budworms and boll weevils See for example, Chem. and Engineering News, May 27, 1985, pp 46-51 and Warthen et al., U.S. Dep. Agric., Agric. Rev. Man., ARM-NE-4. Neem seed extract is considered to be a broad-spectrum insecticide.
Several active compounds have been identified in the seeds.
In J. Insect Physiol., 17: 969-977 (1971) an investigation of the locust feeding inhibition of the seeds of the neem tree, Azadirachta Indica A. Juss and the isolation of a major constituent, azadirachtin, is disclosed. No chemical derivatives of azadirachtin are disclosed.
In J. Chem. Soc. Perkin Trans. I, 2445-2450 (1972) a proposed structure of azadirachtin and its functional groups is disclosed. The preparation of dihydroazadirachtin and a non-reproducible preparation of tetrahydroazadirachtin are also disclosed. No biological activity for the derivatives of azadirachtin is disclosed.
In Proc. 1st Int. Neem Conf., Rottach-Egern, 43-52 (1980) certain biological properties of azadirachtin and some of its derivatives are disclosed. Hydrogenation of the double bond of the dihydrofuran ring is disclosed to have little or no effect on the biological activity of azadirachtin. Removal of the acetyl group is also to have little or no effect on the biological activity.
In Chem. Commun., 46 (1986) the structures of azadirachtin, dihydroazadirachtin and tetrahydroazadirachtin are disclosed. No biological activity is disclosed for those compounds.
In abstracts of the 3rd Int. Neem Conference, Nairobi, Kenya, 1986, the biological activity of azadirachtins including dihydrogenated chemical derivatives of azadirachtin A and azadirachtin B is disclosed.
In DE 3420 230A a new steroid azadirachtin, isolated from Azadirachta Indica and used as an insecticide, nematicide, disinfectant, fertilizer, antiinflammatory, anti-ulcer agent and cold agent, is disclosed.
In J. Agric. Food Chem., 35, 467-471 (1987) eight derivatives of azadirachtin and their growth inhibitory and lethal activities against Heliothis Virescens are disclosed. None of the derivatives had enhanced activity over azadirachtin.
While azadirachtin has been shown to be active as an insecticide, it has not come into commercial use because it is a highly complex compound which is difficult and expensive to isolate in a pure state.
Crude or partially purified extracts of the neem seed have been found to be effective insecticides in the form of liquid and powdered compositions.
In U.S. Pat. No. 4,556,562, an aqueous storage-stable neem seed extract composition is disclosed and claimed. The patent teaches that adjustment of the pH of the composition to the range of 3.5 to 6.0 is necessary to provide for a stable aqueous composition of the extract.
Notwithstanding the above advances there remains a need for an economical, stable composition effective to control pests.